1. Field of the Invention
The present invention relates to a method and apparatus for catching infrared rays in an on-vehicle signal transmission system such as transceivers and the like using the infrared rays, the system being mounted inside a vehicle.
2. Description of the Related Art
Heretofore, as a means for releasing a user's or driver's both hands from his on-vehicle transceiver to provide a hands-free type on-vehicle transceiver, a transmitter 11 using infrared rays for transmitting a sound and a PTT control signal have been used, as shown in FIG. 3.
In a conventional on-vehicle signal transmission system, as shown in FIGS. 4(A) and 4(B), a light receiving element 12 receives infrared rays issued from the transmitter 11, which is carried by the driver. In construction, the light receiving element 12 is disposed in an appropriate surface of a receiver 13 mounted in a front panel and like members of the vehicle. Such appropriate surface of the receiver 13 is a surface oppositely disposed from the transmitter 11, for example such as an upper surface of the receiver 13 as viewed in FIG. 4(A), or a front surface of the receiver 13 as viewed in FIG. 4(B).
In any of the conventional on-vehicle signal transmission systems each having the above construction, sunlight is apt to directly hit the light receiving element 12. Due to this, the conventional systems often malfunction or become inoperative. Of these conventional systems, one called "Directly-plug-in-cigarette-lighter type" has been widely used since this type of system requires least wiring in installation. However, this type of system is most affected by the direct light of the sun.
As described above, the conventional signal transmission system using the infrared rays is affected by the direct light of the sun, and often becomes inoperative or malfunctions. The principal cause of such malfunction is to be sought in the fact that the light receiving element 12 is completely saturated with the direct light of the sun. In other words, it is possible to discriminate a desired signal from other signals, provided that the light receiving element 12 is not saturated.